The IEEE Libraries And Examples Using Functions

Libraries Using the Library Command VHDL allows libraries defined using: library LibraryName; Here, we specify a search path for the compiler to find different functions. Usually, LibraryName refers to a directory name, where different files are stored. For example: library ieee; refers to the VHDL files that are defined by IEEE. To use specific definitions, we will have to know the name of the file where the definition is find. Here, you can use OS find functions to find a file that contains the definitions. Such files are referred to as package files in VHDL. In these files, you can find important VHDL extensions. We should always consider using any function defined by IEEE, and avoid re-defining any function already given by IEEE.

Simple Examples Here are some of the best known IEEE packages: std_logic_ basic definitions std_logic_arith-- general arithmetic functions std_logic_signed-- signed arithmetic functions std_logic_unsigned-- unsigned arithmetic functions To use the definitions from a package, we need the general commands: library LibraryName; -- "directory" name use LibraryName.packageName.all; -- function definitions For the basic definitions, we use: library ieee; use ieee.std_logic_1164.all;

IEEE Packages math_complex.vhd -- no source code found … math_real.vhd - - no source code found … numeric_bit.vhd -- ΙΕΕΕ file for VHDL synthesis numeric_std.vhd -- ΙΕΕΕ file for VHDL synthesis std_logic_1164.vhd - - basic definitions for digital logic std_logic_arith.vhd -- large collection of arithmetic functions std_logic_signed.vhd -- signed functions for std_logic_vector std_logic_unsigned.vhd -- unsigned functions for std_logic_vector std_logic_misc.vhd - - miscellaneous std_logic_textio.vhd - - text file processing We will explore some of them in detail.

Definition of std_ulogic TYPE std_ulogic IS ( 'U', -- Uninitialized 'X', -- Forcing Unknown '0', -- Forcing 0 '1', -- Forcing 1 'Z', -- High Impedance 'W', -- Weak Unknown 'L', -- Weak 0 'H', -- Weak 1 '-' -- Don't care ); To understand how these work, we will study the and function …

Basic Data Types (Ι/ΙΙ) unconstrained array of std_ulogic for use with the resolution function TYPE std_ulogic_vector IS ARRAY ( NATURAL RANGE <> ) OF std_ulogic; resolution function FUNCTION resolved ( s : std_ulogic_vector ) RETURN std_ulogic; *** industry standard logic type *** SUBTYPE std_logic IS resolved std_ulogic; unconstrained array of std_logic for use in declaring signal arrays TYPE std_logic_vector IS ARRAY ( NATURAL RANGE <>) OF std_logic;

Basic Data Types (ΙΙ/ΙΙ) common subtypes SUBTYPE X01 IS resolved std_ulogic RANGE 'X' TO '1'; -- ('X','0','1') SUBTYPE X01Z IS resolved std_ulogic RANGE 'X' TO 'Z'; -- ('X','0','1','Z') SUBTYPE UX01 IS resolved std_ulogic RANGE 'U' TO '1'; -- ('U','X','0','1') SUBTYPE UX01Z IS resolved std_ulogic RANGE 'U' TO 'Z'; -- ('U','X','0','1','Z')

Basic Functions For std_ulogic FUNCTION "and" ( l : std_ulogic; r : std_ulogic ) RETURN UX01; FUNCTION "nand" ( l : std_ulogic; r : std_ulogic ) RETURN UX01; FUNCTION "or" ( l : std_ulogic; r : std_ulogic ) RETURN UX01; FUNCTION "nor" ( l : std_ulogic; r : std_ulogic ) RETURN UX01; FUNCTION "xor" ( l : std_ulogic; r : std_ulogic ) RETURN UX01; function "xnor" ( l : std_ulogic; r : std_ulogic ) return ux01; FUNCTION "not" ( l : std_ulogic ) RETURN UX01;

Basic Functions for Vectors vectorized overloaded logical operators FUNCTION "and" ( l, r : std_logic_vector ) RETURN std_logic_vector; FUNCTION "and" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; FUNCTION "nand" ( l, r : std_logic_vector ) RETURN std_logic_vector; FUNCTION "nand" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; FUNCTION "or" ( l, r : std_logic_vector ) RETURN std_logic_vector; FUNCTION "or" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; FUNCTION "nor" ( l, r : std_logic_vector ) RETURN std_logic_vector; FUNCTION "nor" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; FUNCTION "xor" ( l, r : std_logic_vector ) RETURN std_logic_vector; FUNCTION "xor" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; function "xnor" ( l, r : std_logic_vector ) return std_logic_vector; function "xnor" ( l, r : std_ulogic_vector ) return std_ulogic_vector; FUNCTION "not" ( l : std_logic_vector ) RETURN std_logic_vector; FUNCTION "not" ( l : std_ulogic_vector ) RETURN std_ulogic_vector;

Rising and Falling Edges for the Clock edge detection FUNCTION rising_edge (SIGNAL s : std_ulogic) RETURN BOOLEAN; FUNCTION falling_edge (SIGNAL s : std_ulogic) RETURN BOOLEAN;

A Simple Example Function: "and" TYPE stdlogic_table IS ARRAY(std_ulogic, std_ulogic) OF std_ulogic; -- truth table for "and" function CONSTANT and_table : stdlogic_table := ( | U X 0 1 Z W L H - | | ( 'U', 'U', '0', 'U', 'U', 'U', '0', 'U', 'U' ), -- | U | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ), -- | X | ( '0', '0', '0', '0', '0', '0', '0', '0', '0' ), -- | 0 | ( 'U', 'X', '0', '1', 'X', 'X', '0', '1', 'X' ), -- | 1 | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ), -- | Z | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ), -- | W | ( '0', '0', '0', '0', '0', '0', '0', '0', '0' ), -- | L | ( 'U', 'X', '0', '1', 'X', 'X', '0', '1', 'X' ), -- | H | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ) -- | - | ); -- Note that the outputs are only: U, X, 0, L and 0 force the output to be A 1-input copies the input to the output, replacing with X. FUNCTION "and" ( l : std_ulogic; r : std_ulogic ) RETURN UX01 IS BEGIN RETURN (and_table(l, r)); -- note the use of the table! END "and";

The STD_LOGIC_ARITH Package -- Copyright (c) 1990,1991,1992 by Synopsys, Inc. All rights reserved. --Package name: STD_LOGIC_ARITH Purpose: A set of arithemtic, conversion, and comparison functions for SIGNED, UNSIGNED, SMALL_INT, INTEGER, STD_ULOGIC, STD_LOGIC, and STD_LOGIC_VECTOR. package std_logic_arith is type UNSIGNED is array (NATURAL range <>) of STD_LOGIC; type SIGNED is array (NATURAL range <>) of STD_LOGIC; subtype SMALL_INT is INTEGER range 0 to 1; function "+"(L: UNSIGNED; R: UNSIGNED) return UNSIGNED; function "+"(L: SIGNED; R: SIGNED) return SIGNED;

Examples of Simple Functions for UNSIGNED Inputs function "-"(L: UNSIGNED; R: UNSIGNED) return UNSIGNED; function "+"(L: UNSIGNED) return UNSIGNED; function "ABS"(L: SIGNED) return SIGNED; function "*"(L: UNSIGNED; R: SIGNED) return SIGNED; function "<"(L: UNSIGNED; R: UNSIGNED) return BOOLEAN; function "<="(L: UNSIGNED; R: UNSIGNED) return BOOLEAN; function ">"(L: UNSIGNED; R: UNSIGNED) return BOOLEAN; function ">="(L: UNSIGNED; R: UNSIGNED) return BOOLEAN; function "="(L: UNSIGNED; R: UNSIGNED) return BOOLEAN; function "/="(L: UNSIGNED; R: UNSIGNED) return BOOLEAN;

Functions for Conversions and Shifts function SHL(ARG: UNSIGNED; COUNT: UNSIGNED) return UNSIGNED; function SHL(ARG: SIGNED; COUNT: UNSIGNED) return SIGNED; function SHR(ARG: UNSIGNED; COUNT: UNSIGNED) return UNSIGNED; function SHR(ARG: SIGNED; COUNT: UNSIGNED) return SIGNED; function CONV_STD_LOGIC_VECTOR(ARG: INTEGER; SIZE: INTEGER) return STD_LOGIC_VECTOR; function CONV_STD_LOGIC_VECTOR(ARG: UNSIGNED; SIZE: INTEGER) return STD_LOGIC_VECTOR; function CONV_STD_LOGIC_VECTOR(ARG: SIGNED; SIZE: INTEGER) return STD_LOGIC_VECTOR; function CONV_STD_LOGIC_VECTOR(ARG: STD_ULOGIC; SIZE: INTEGER) return STD_LOGIC_VECTOR;

Arithmetic Functions function mult(A,B: SIGNED) return SIGNED; function mult(A,B: UNSIGNED) return UNSIGNED; function plus(A, B: SIGNED) return SIGNED; function unsigned_plus(A, B: UNSIGNED) return UNSIGNED; function minus(A, B: SIGNED) return SIGNED; function unsigned_minus(A, B: UNSIGNED) return UNSIGNED; function is_less(A, B: SIGNED) return BOOLEAN; function is_less_or_equal(A, B: SIGNED) return BOOLEAN; function unsigned_is_less(A, B: UNSIGNED) return BOOLEAN; function unsigned_is_less_or_equal(A, B: UNSIGNED) return BOOLEAN;

The STD_LOGIC_SIGNED Package -- Copyright (c) 1990, 1991, 1992 by Synopsys, Inc All rights reserved Package name: STD_LOGIC_SIGNED -- function "+"(L: STD_LOGIC; R: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function "ABS"(L: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function "*"(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function "<"(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function "<="(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function ">"(L: INTEGER; R: STD_LOGIC_VECTOR) return BOOLEAN; function ">="(L: INTEGER; R: STD_LOGIC_VECTOR) return BOOLEAN; function "="(L: INTEGER; R: STD_LOGIC_VECTOR) return BOOLEAN; function "/="(L: INTEGER; R: STD_LOGIC_VECTOR) return BOOLEAN; function SHL(ARG:STD_LOGIC_VECTOR;COUNT: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function SHR(ARG:STD_LOGIC_VECTOR;COUNT: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function CONV_INTEGER(ARG: STD_LOGIC_VECTOR) return INTEGER;

The STD_LOGIC_UNSIGNED Package -- Copyright (c) 1990, 1991, 1992 by Synopsys, Inc. --Package name: STD_LOGIC_UNSIGNED package STD_LOGIC_UNSIGNED is function "-"(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function "+"(L: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function "*"(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function "<"(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function "<="(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function ">"(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function ">="(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function "="(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function "/="(L: STD_LOGIC_VECTOR; R: STD_LOGIC_VECTOR) return BOOLEAN; function SHL(ARG:STD_LOGIC_VECTOR;COUNT: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function SHR(ARG:STD_LOGIC_VECTOR;COUNT: STD_LOGIC_VECTOR) return STD_LOGIC_VECTOR; function CONV_INTEGER(ARG: STD_LOGIC_VECTOR) return INTEGER;